The present invention relates to a method and a device for modifying the torque of an internal combustion engine having at least one first cylinder with an exhaust valve having a variable valve control.
Internal combustion engines, in particular for motor vehicles, may operate with one or more camshafts to control the engine valves according to a predetermined stroke sequence, and the stroke sequence may be specified by the mechanical structure of the camshaft. However, a specified stroke sequence may not permit optimal engine performance because different engine operating states in general require different stroke sequences.
In this regard, internal combustion engines having a hydraulic or electromagnetic camless valve drive instead of a rigid mechanical arrangement may constitute an advance in the design of valve controls. In a camless internal combustion engine, the amount of intake air and residual exhaust gas in each cylinder may be controlled by modifying the time of opening and/or closing of the intake and exhaust valves.
For these conventional internal combustion engines, the following control actions may be known for influencing, in a controlled manner, the torque delivered by the internal combustion engine.
First, with spark ignition engines in particular, a filling intervention may be carried out, modifying the gas filling of the cylinder via an electrically controllable throttle valve or a bypass controller. This filling intervention may be designed to be approximately neutral with regard to consumption or exhaust emissions, but the filling intervention may produce only a gradual change in torque and may not permit any change in the torque contribution of the cylinder during an operating cycle after closing the intake valves of the cylinder. Because of the gradual change, it may not be possible to have high quality idling, i.e., constant idling through the filling intervention alone.
The second method is a filling intervention via the intake valves of the corresponding cylinders with variable intake valve control. As in the case of the filling intervention via the electric throttle valve or the bypass controller, this control action may permit a setting which is approximately neutral with regard to consumption and emissions. However, the filling intervention involving the intake valves is also slow and may not allow any change in torque contribution during a working cycle after closing the intake valve of the respective cylinder.
A third method is a firing angle intervention. Firing angle intervention essentially makes it possible to influence the torque contribution of the respective cylinder and thus the torque of the internal combustion engine after the intake valve of the respective cylinder is closed, by making an adjustment, usually by delaying the firing angle. However, modifying the firing angle may have a negative effect on combustion in the cylinder, leading to increased fuel consumption and possibly also greater exhaust emissions. Furthermore, with this firing angle intervention, the adjustment options may be very minor, depending on the combustion method and the operating point of the internal combustion engine because reliable and stable ignition and combustion are necessary for reasons of fuel consumption, exhaust emissions and smooth running. Furthermore, although the firing angle intervention may be comparatively rapid, it may not allow any change in torque contribution during a working cycle after the beginning of combustion in the respective cylinder.
Finally, there may be injection measures through which the quantity of fuel supplied may be varied. This may provide a relatively quick modification in torque of the internal combustion engine, but the change cannot be implemented during ongoing combustion within a working cycle.
The individual combustion processes in the individual cylinders of the internal combustion engine may be subject to cyclic fluctuations in combustion. These cyclic combustion fluctuations may result from stochastic fluctuations in the local composition and kinematics of the individual fuel-air mixtures in the area of the spark plug at the time of ignition and their influences on the formation of the flame core and the duration of the ignition phase. This may result in different contributions of the individual cylinders to the torque of the internal combustion engine. These differences in individual torque contributions may result in out-of-true running of the internal combustion engine and in particular to poor idling quality. Moreover, the differences cause unnecessary fuel consumption and increased exhaust emissions.
Since all the control actions described above are carried out before the start of combustion in the respective cylinder, they may not be suitable for control, in particular for equalization of the individual torque contributions of the individual cylinders. The interventions referred to above may not suitable for compensating for cyclic fluctuations in combustion because they may not respond to changes or influences occurring during combustion within a working cycle, but instead they produce changes in the following working cycle of the following cylinder at the soonest.
An object of an exemplary embodiment and/or exemplary method of the present invention is to provide a method and a device for rapidly changing the torque of an internal combustion engine having at least one cylinder with an exhaust valve having a variable valve control.
In an exemplary method for modifying the torque of an internal combustion engine having at least one first cylinder with an exhaust valve having a variable valve control according to the present invention, a determination is made as to whether there may be a demand for modifying the torque within a first working cycle of the first cylinder, and if it is determined that it may be necessary to modify the torque during the first working cycle, a basic triggering of the exhaust valve of the first cylinder may be modified in the first working cycle.
A demand determining device for determining whether there may be a demand for modifying the torque within the first working cycle of the first cylinder is provided in a device according to an exemplary embodiment of the present invention, and there is a triggering modifying device that modifies the basic triggering of the exhaust valve of the first cylinder in the first working cycle when the demand determining device determines that the torque should be modified.
An exemplary embodiment and/or exemplary method of the present invention provides a method and/or a device by which the torque contribution of the corresponding cylinder and thus the torque of the internal combustion engine may be modified very quickly, even within the same working cycle of the respective cylinder. In this way it may be possible to achieve high idling quality. Moreover, the exemplary method and exemplary device may minimize or at least reduce any difference between individual torque contributions of individual cylinders, and thus achieve a high quality average pressure equalization of the individual cylinders among one another and a very good constancy of the average torque contribution of successive working cycles in steady-state operation.
Furthermore, the exemplary method and/or the exemplary device according to the present invention may permit a change in torque of an internal combustion engine when it may no longer be possible to perform a filling intervention via the throttle valve or a filling intervention using the intake valves, a firing angle measure or injection measure, in particular when combustion is already underway. On the whole, this may provide engine operation that is improved in both steady-state and non-steady-state operation with regard to target parameters, such as fuel consumption, exhaust emissions and smooth running in particular.
An exemplary embodiment and/or exemplary method of the present invention may permit the basic triggering of the exhaust valves to be modified with regard to at least one of a plurality of opening parameters, in which the plurality of opening parameters includes at least one opening angle of the exhaust valve, one opening lift of the exhaust valve and one opening rate of the exhaust valve, and the control modifying device is designed to modify at least one of the plurality of opening parameters mentioned above. This may provide a simple and flexible way of modifying the torque.
In another exemplary embodiment and/or exemplary method of the present invention, a determination is made on the basis of at least one of a plurality of setpoint values, changes in which may have an effect on the torque delivered by the internal combustion engine, to determine whether there may be a demand for a change in the torque. This may provide a simple determination of the demand of whether or not the torque should be modified within the first working cycle.
In another exemplary embodiment and/or exemplary method of the present invention, the plurality of setpoint values includes instantaneous values and changes in time from a setpoint torque of the internal combustion engine, a setpoint torque of the first cylinder to the torque of the internal combustion engine, an efficiency of the internal combustion engine and an efficiency of the first cylinder. This may provide an accurate determination of whether or not there may be a demand for a change in the torque in the first working cycle because the setpoint torque of the internal combustion engine may be detected by an accelerator pedal position sensor, for example, in a motor vehicle.
In another exemplary embodiment and/or exemplary method of the present invention, the demand for a modification in torque is determined on the basis of at least one of a plurality of internal combustion engine status parameters which are detected by at least one detection device. This may provide a rapid response to changes occurring within the internal combustion engine, such as incomplete combustion in a cylinder, for example.
In another exemplary embodiment and/or exemplary method of the present invention, the plurality of internal combustion engine status parameters includes the position and height of the maximum pressure of the first torque contribution of the first cylinder to the torque of the internal combustion engine, a combustion chamber pressure and a variation of the combustion chamber pressure in the first cylinder. This may provide a direct response to changes in the combustion process in the internal combustion engine because the demand is determined on the basis of internal combustion engine status parameters, which depend directly on the combustion process taking place in the first cylinder during the first working cycle.
In another exemplary embodiment and/or exemplary method of the present invention, the basic triggering is determined by a control device on the basis of at least one firing angle of the first cylinder, a fuel mass and an air mass, which may be supplied to the first cylinder.
Determination of the basic triggering on the basis of the firing angle of the air mass and the fuel mass supplied may provide a precise and accurate determination of the basic triggering of the exhaust valve of the first cylinder.
In another exemplary embodiment and/or exemplary method of the present invention, a first torque contribution of the first cylinder to the torque of the internal combustion engine in the first working cycle of the first cylinder is compared with a second torque contribution of a second cylinder to the torque of the internal combustion engine in a second working cycle of the second cylinder, and a demand for a change in the torque of the internal combustion engine within the first working cycle of the first cylinder is determined when the first torque contribution is not equal to the second torque contribution, and the basic triggering of the exhaust valve of the first cylinder changes in the first working cycle in such a way that the first and second torque contributions are matched, with a beginning of the first working cycle occurring chronologically after a beginning of the second working cycle. This may minimize the difference between the torque contributions of the individual cylinders to the torque of the internal combustion engine. This may provide a high idling quality and a high quality of the average pressure equalization of the cylinders among one another and a good constancy of the average pressure of successive working cycles in steady-state operation. On the whole, this may result in very smooth running, in particular when the internal combustion engine is idling.
In another exemplary embodiment and/or exemplary method of the present invention, the basic triggering of the exhaust valve of the first cylinder is modified regardless of whether or not a demand for a change in the torque of the internal combustion engine has been determined, so that the first torque contribution of the first cylinder to the torque of the internal combustion engine is less than a maximum instantaneous contribution of the first cylinder. Thus, the basic triggering of the exhaust valve is modified, regardless of whether or not there may be a demand for a change in the torque of the internal combustion engine, so that the resulting torque contribution of the cylinder may be lower than the torque contribution of the cylinder that would have been achieved by using the basic triggering, which may aim at the maximum torque contribution. In other words, controlled triggering of the exhaust valve may have a negative effect on the internal engine efficiency. This is referred to as a derivative action. Use of such a derivative action basic setting, i.e., a torque that is reduced in comparison with the normal basic setting, may permit a rapid increase in torque if necessary. This may also provide a further improvement in the smoothness of running and in the idling quality of the internal combustion engine.